We firstly describe derivation of this action, following [1]}. Let us introduce relativistic vielbein \(e_M^{ \ \underline{a}}\)  so that
target space metric has the form
\(g_{MN}=e_M^{ \ \underline{a}}e_N^{ \ \underline{b}}\eta _{\underline{a}\underline{b}} \ ,\) 
